Aspects of the present disclosure relate generally to wireless communications, and more particularly, to physical layer procedures at a wireless device.
Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, etc. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources. Examples of such multiple-access networks include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA) networks.
These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example of an emerging telecommunication standard is Long Term Evolution (LTE). LTE is a set of enhancements to the UMTS mobile standard promulgated by Third Generation Partnership Project (3GPP). It is designed to better support mobile broadband Internet access by improving spectral efficiency, lower costs, improve services, make use of new spectrum, and better integrate with other open standards using OFDMA on the downlink (DL), SC-FDMA on the uplink (UL), and multiple-input multiple-output (MIMO) antenna technology. However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in LTE technology. Preferably, these improvements should be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.
A wireless communication network may include a number of eNodeBs that can support communication for a number of user equipments (UEs). A UE may communicate with an eNodeB via the downlink and uplink. The downlink (or forward link) refers to the communication link from the eNodeB to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the eNodeB.
Operation of wireless devices in certain portions of a shared or unlicensed spectrum may experience interference from another radio access technology (RAT) using the spectrum. For example, both LTE and Wi-Fi may operate in an unlicensed 5 GHz band. Over-the-air interference detection is employed in some wireless communication networks in an attempt to mitigate such interference. For example, a device may periodically monitor (e.g., sniff) for energy in the RF band used by the device. Upon detection of any kind of energy, the device may back-off the RF band for a period of time. Such process may be referred to as clear channel assessment (CCA).
In practice, however, there may be problems with such a back-off or “listen-before-talk” (LBT) approach. Some transmissions may be delayed or may not occur due to CCA procedures. For example, an eNodeB may not transmit various reference signals in the downlink due to CCA procedures. A UE may be unable to correctly measure the downlink channel of an eNodeB when reference signals are missing. Missing or inaccurate measurements may cause further problems for radio resource monitoring, radio link monitoring, and radio link failure detection. In view of the foregoing, it may be understood that there may be significant problems and shortcomings associated with operation of wireless devices in shared and unlicensed spectrum.